Carbon nanotubes (CNTs) were discovered in 1991 in the soot of a fullerene generator in which under certain reaction conditions, tube-like structures with a diameter of only several tens of nanometers, but with a length of several micrometers were present.
CNTs are part of the family of fullerenes and their walls consist, like those of fullerenes or like the planes of graphite, only of carbon, whereby the carbon atoms have a honeycomb-like structure with six corners. The diameter of the tubes is mostly in a range between 1 and 50 nm. Lengths of several millimeters for individual tubes and of up to 20 cm for tube bundles have been achieved.
Several outstanding properties of CNTs are, for example, their mechanical tensile strength and stiffness of about 40 GPa and 1 TPa, respectively (20 times and 5 times greater than that of steel). The current-carrying capacity and the thermal conductivity are also of interest. The current-carrying capacity of CNTs is approximately 1000 times greater than that of copper wires and the thermal conductivity at room temperature is about 6000 W/m*K, approximately twice that of diamond, the best naturally occurring thermal conductor.
Yarns built from CNTs are under development for use in electrical conductors to take advantage of the numerous desirable properties exhibited by CNTs. Twisted or braided yarns of CNT are being investigated to form larger diameter conductors to replace traditional copper wire, particularly in applications in which weight reduction is important, such as in spacecraft and aircraft applications.
Among the challenges associated with the use of CNT yarns as electrical conductors is the occurrence of splitting or unfolding of those yarns when cut or trimmed. Such fraying can result in difficulty inserting the conductor into terminals. In addition, high impurity or residual catalyst content in the CNT yarns that are currently commercially available can result in non-uniform mechanical and electrical performance. That in turn can result in discontinuities or circuitous travel along the electrical path of the yarn. Those contaminants also make the conductor susceptible to environmental effects, such as corrosion and thermal degradation.
These and other drawbacks are found in the use of CNTs as electrical conductors.